Metamaterials are artificial materials engineered to include at least one artificial atom unit that is patterned in a random size and shape smaller than the wavelength, wherein the metamaterials are structured by an array of the artificial atom units. Each of the artificial atom units included in the metamaterials exhibits predetermined properties in response to electromagnetic waves or acoustic waves applied to the metamaterials.
Consequently, metamaterials may be provided to have any effective refractive index and effective material coefficient that are not readily observed in nature with regard to electromagnetic waves or acoustic waves. Thereby, the metamaterials give rise to many novel phenomena including subwavelength focusing, negative refraction, extraordinary transmission, invisibility cloaking, or the like.
Phenomena caused by the metamaterials also occur in photonic or phononic crystals. However, in this case, the phenomena with regard to the photonic or phononic crystals occur only near the diffraction region where operating frequencies are high. It is hard to expect an application using the effective material coefficient. That is, the size of an artificial atom is constrained not to be sufficiently small in comparison with the wavelength.